Encode connection attribute only once.

connection.go

@@ -27,6 +27,7 @@ type mysqlConn struct {
 	affectedRows     uint64
 	insertId         uint64
 	cfg              *Config
+	connector        *connector
 	maxAllowedPacket int
 	maxWriteSize     int
 	writeTimeout     time.Duration

connector.go

@@ -11,11 +11,54 @@ package mysql
 import (
 	"context"
 	"database/sql/driver"
+	"fmt"
 	"net"
+	"os"
+	"strconv"
+	"strings"
 )
 
 type connector struct {
-	cfg *Config // immutable private copy.
+	cfg               *Config // immutable private copy.
+	encodedAttributes string  // Encoded connection attributes.
+}
+
+func encodeConnectionAttributes(textAttributes string) string {
+	connAttrsBuf := make([]byte, 0, 251)
+
+	// default connection attributes
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrClientName)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrClientNameValue)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrOS)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrOSValue)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPlatform)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPlatformValue)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPid)
+	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, strconv.Itoa(os.Getpid()))
+
+	// user-defined connection attributes
+	for _, connAttr := range strings.Split(textAttributes, ",") {
+		attr := strings.SplitN(connAttr, ":", 2)
+		if len(attr) != 2 {
+			continue
+		}
+		for _, v := range attr {
+			connAttrsBuf = appendLengthEncodedString(connAttrsBuf, v)
+		}
+	}
+
+	return string(connAttrsBuf)
+}
+
+func newConnector(cfg *Config) (*connector, error) {
+	encodedAttributes := encodeConnectionAttributes(cfg.ConnectionAttributes)
+	if len(encodedAttributes) > 250 {
+		return nil, fmt.Errorf("connection attributes are longer than 250 bytes: %dbytes (%q)", len(encodedAttributes), cfg.ConnectionAttributes)
+	}
+	return &connector{
+		cfg:               cfg,
+		encodedAttributes: encodedAttributes,
+	}, nil
 }
 
 // Connect implements driver.Connector interface.
@@ -29,6 +72,7 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 		maxWriteSize:     maxPacketSize - 1,
 		closech:          make(chan struct{}),
 		cfg:              c.cfg,
+		connector:        c,
 	}
 	mc.parseTime = mc.cfg.ParseTime
 

connector_test.go

@@ -8,13 +8,16 @@ import (
 )
 
 func TestConnectorReturnsTimeout(t *testing.T) {
-	connector := &connector{&Config{
+	connector, err := newConnector(&Config{
 		Net:     "tcp",
 		Addr:    "1.1.1.1:1234",
 		Timeout: 10 * time.Millisecond,
-	}}
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
 
-	_, err := connector.Connect(context.Background())
+	_, err = connector.Connect(context.Background())
 	if err == nil {
 		t.Fatal("error expected")
 	}

driver.go

@@ -85,8 +85,9 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 	if err != nil {
 		return nil, err
 	}
-	c := &connector{
-		cfg: cfg,
+	c, err := newConnector(cfg)
+	if err != nil {
+		return nil, err
 	}
 	return c.Connect(context.Background())
 }
@@ -103,7 +104,7 @@ func NewConnector(cfg *Config) (driver.Connector, error) {
 	if err := cfg.normalize(); err != nil {
 		return nil, err
 	}
-	return &connector{cfg: cfg}, nil
+	return newConnector(cfg)
 }
 
 // OpenConnector implements driver.DriverContext.
@@ -112,7 +113,5 @@ func (d MySQLDriver) OpenConnector(dsn string) (driver.Connector, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &connector{
-		cfg: cfg,
-	}, nil
+	return newConnector(cfg)
 }

packets.go

@@ -18,9 +18,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"os"
-	"strconv"
-	"strings"
 	"time"
 )
 
@@ -322,31 +319,12 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 		pktLen += n + 1
 	}
 
-	connAttrsBuf := make([]byte, 0, 100)
-
-	// default connection attributes
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrClientName)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrClientNameValue)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrOS)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrOSValue)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPlatform)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPlatformValue)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPid)
-	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, strconv.Itoa(os.Getpid()))
-
-	// user-defined connection attributes
-	for _, connAttr := range strings.Split(mc.cfg.ConnectionAttributes, ",") {
-		attr := strings.Split(connAttr, ":")
-		if len(attr) != 2 {
-			continue
-		}
-		for _, v := range attr {
-			connAttrsBuf = appendLengthEncodedString(connAttrsBuf, v)
-		}
-	}
-
 	// 1 byte to store length of all key-values
-	pktLen += len(connAttrsBuf) + 1
+	// NOTE: Actually, this is length encoded integer.
+	// But we support only len(connAttrBuf) < 251 for now because takeSmallBuffer
+	// doesn't support buffer size more than 4096 bytes.
+	// TODO(methane): Rewrite buffer management.
+	pktLen += 1 + len(mc.connector.encodedAttributes)
 
 	// Calculate packet length and get buffer with that size
 	data, err := mc.buf.takeSmallBuffer(pktLen + 4)
@@ -425,9 +403,9 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 	pos++
 
 	// Connection Attributes
-	data[pos] = byte(len(connAttrsBuf))
+	data[pos] = byte(len(mc.connector.encodedAttributes))
 	pos++
-	pos += copy(data[pos:], connAttrsBuf)
+	pos += copy(data[pos:], []byte(mc.connector.encodedAttributes))
 
 	// Send Auth packet
 	return mc.writePacket(data[:pos])

packets_test.go

@@ -96,9 +96,14 @@ var _ net.Conn = new(mockConn)
 
 func newRWMockConn(sequence uint8) (*mockConn, *mysqlConn) {
 	conn := new(mockConn)
+	connector, err := newConnector(NewConfig())
+	if err != nil {
+		panic(err)
+	}
 	mc := &mysqlConn{
 		buf:              newBuffer(conn),
-		cfg:              NewConfig(),
+		cfg:              connector.cfg,
+		connector:        connector,
 		netConn:          conn,
 		closech:          make(chan struct{}),
 		maxAllowedPacket: defaultMaxAllowedPacket,